InvalidCastException F# snippets (#7772)

Author: albert-du

snippets/fsharp/System/InvalidCastException/Overview/Interface1.fs

@@ -0,0 +1,17 @@
+module Interface1
+
+// <Snippet3>
+open System
+open System.Globalization
+
+let culture = CultureInfo.InvariantCulture
+let provider: IFormatProvider = culture
+
+let dt = provider :?> DateTimeFormatInfo
+
+// The example displays the following output:
+//    Unhandled Exception: System.InvalidCastException:
+//       Unable to cast object of type //System.Globalization.CultureInfo// to
+//           type //System.Globalization.DateTimeFormatInfo//.
+//       at Example.main()
+// </Snippet3>

snippets/fsharp/System/InvalidCastException/Overview/ToString1.fs

@@ -0,0 +1,7 @@
+module ToString1
+
+// <Snippet4>
+let value: obj = 12
+// Cast throws an InvalidCastException exception.
+let s = value :?> string
+// </Snippet4>

snippets/fsharp/System/InvalidCastException/Overview/ToString2.fs

@@ -0,0 +1,9 @@
+module ToString2
+
+// <Snippet5>
+let value: obj = 12
+let s = value.ToString()
+printfn $"{s}"
+// The example displays the following output:
+//      12
+// </Snippet5>

snippets/fsharp/System/InvalidCastException/Overview/basetoderived1.fs

@@ -0,0 +1,35 @@
+module basetoderived1
+
+// <Snippet1>
+open System
+
+type Person() =
+    member val Name = String.Empty with get, set
+
+type PersonWithId() =
+    inherit Person()
+    member val Id = String.Empty with get, set
+
+
+let p = Person()
+p.Name <- "John"
+try
+    let pid = p :?> PersonWithId
+    printfn "Conversion succeeded."
+with :? InvalidCastException ->
+    printfn "Conversion failed."
+
+let pid1 = PersonWithId()
+pid1.Name <- "John"
+pid1.Id <- "246"
+let p1: Person = pid1
+try
+    let pid1a = p1 :?> PersonWithId
+    printfn "Conversion succeeded."
+with :? InvalidCastException ->
+    printfn "Conversion failed."
+
+// The example displays the following output:
+//       Conversion failed.
+//       Conversion succeeded.
+// </Snippet1>

snippets/fsharp/System/InvalidCastException/Overview/fs.fsproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="iconvertible1.fs" />
+    <Compile Include="basetoderived1.fs" />
+    <Compile Include="Interface1.fs" />
+    <Compile Include="ToString1.fs" />
+    <Compile Include="ToString2.fs" />
+  </ItemGroup>
+</Project>

snippets/fsharp/System/InvalidCastException/Overview/iconvertible1.fs

@@ -0,0 +1,23 @@
+module iconvertible1
+
+// <Snippet2>
+open System
+
+let flag = true
+try
+    let conv: IConvertible = flag
+    let ch = conv.ToChar null
+    printfn "Conversion succeeded."
+with :? InvalidCastException ->
+    printfn "Cannot convert a Boolean to a Char."
+
+try
+    let ch = Convert.ToChar flag
+    printfn "Conversion succeeded."
+with :? InvalidCastException ->
+    printfn "Cannot convert a Boolean to a Char."
+
+// The example displays the following output:
+//       Cannot convert a Boolean to a Char.
+//       Cannot convert a Boolean to a Char.
+// </Snippet2>

xml/System/InvalidCastException.xml

@@ -100,6 +100,7 @@ For a list of initial property values for an instance of <xref:System.InvalidCas
  You directly or indirectly call a primitive type's <xref:System.IConvertible> implementation that does not support a particular conversion. For example, trying to convert a <xref:System.Boolean> value to a <xref:System.Char> or a <xref:System.DateTime> value to an <xref:System.Int32> throws an <xref:System.InvalidCastException> exception. The following example calls both the <xref:System.Boolean.System%23IConvertible%23ToChar%2A?displayProperty=nameWithType> and <xref:System.Convert.ToChar%28System.Boolean%29?displayProperty=nameWithType> methods to convert a <xref:System.Boolean> value to a <xref:System.Char>. In both cases, the method call throws an <xref:System.InvalidCastException> exception.
 
  :::code language="csharp" source="~/snippets/csharp/System/InvalidCastException/Overview/iconvertible1.cs" interactive="try-dotnet" id="Snippet2":::
+ :::code language="fsharp" source="~/snippets/fsharp/System/InvalidCastException/Overview/iconvertible1.fs" id="Snippet2":::
  :::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.invalidcastexception/vb/iconvertible1.vb" id="Snippet2":::
 
  Because the conversion is not supported, there is no workaround.
@@ -123,6 +124,7 @@ For a list of initial property values for an instance of <xref:System.InvalidCas
  You are downcasting, that is, trying to convert an instance of a base type to one of its derived types. In the following example, trying to convert a `Person` object to a `PersonWithID` object fails.
 
  :::code language="csharp" source="~/snippets/csharp/System/InvalidCastException/Overview/basetoderived1.cs" interactive="try-dotnet" id="Snippet1":::
+ :::code language="fsharp" source="~/snippets/fsharp/System/InvalidCastException/Overview/basetoderived1.fs" id="Snippet1":::
  :::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.invalidcastexception/vb/basetoderived1.vb" id="Snippet1":::
 
  As the example shows, the downcast succeeds only if the `Person` object was created by an upcast from a `PersonWithId` object to a `Person` object, or if the `Person` object is `null`.
@@ -132,6 +134,7 @@ For a list of initial property values for an instance of <xref:System.InvalidCas
  You are attempting to convert an interface object to a type that  implements that interface, but the target type is not the same type or a base class of the type from which the interface object was originally derived. The following example throws an <xref:System.InvalidCastException> exception when it attempts to convert an <xref:System.IFormatProvider> object  to a <xref:System.Globalization.DateTimeFormatInfo> object. The conversion fails because although the <xref:System.Globalization.DateTimeFormatInfo> class implements the <xref:System.IFormatProvider> interface, the <xref:System.Globalization.DateTimeFormatInfo> object is not related to the <xref:System.Globalization.CultureInfo> class from which  the interface object was derived.
 
  :::code language="csharp" source="~/snippets/csharp/System/InvalidCastException/Overview/Interface1.cs" id="Snippet3":::
+ :::code language="fsharp" source="~/snippets/fsharp/System/InvalidCastException/Overview/Interface1.fs" id="Snippet3":::
  :::code language="vb" source="~/snippets/visualbasic/VS_Snippets_CLR_System/system.invalidcastexception/vb/Interface1.vb" id="Snippet3":::
 
  As the exception message indicates, the conversion would succeed only if the interface object is converted back to an instance of the original type, in this case a  <xref:System.Globalization.CultureInfo>. The conversion would also succeed if the interface object is converted to an instance of a base type of the original type.
@@ -141,13 +144,15 @@ For a list of initial property values for an instance of <xref:System.InvalidCas
  You are trying to convert a value or an object to its string representation by using a casting operator in C#. In the following example, both the attempt to cast a <xref:System.Char> value to a string and the attempt to cast an integer to a string throw an <xref:System.InvalidCastException> exception.
 
  :::code language="csharp" source="~/snippets/csharp/System/InvalidCastException/Overview/ToString1.cs" id="Snippet4":::
+ :::code language="fsharp" source="~/snippets/fsharp/System/InvalidCastException/Overview/ToString1.fs" id="Snippet4":::
 
 > [!NOTE]
 >  Using the Visual Basic `CStr` operator to convert a value of a primitive type to a string succeeds. The operation does not throw an <xref:System.InvalidCastException> exception.
 
  To successfully convert an instance of any type to its string representation, call its `ToString` method, as the following example does. The `ToString` method is always present, since the <xref:System.Object.ToString%2A> method is defined by the <xref:System.Object> class and therefore is either inherited or overridden by all managed types.
 
  :::code language="csharp" source="~/snippets/csharp/System/InvalidCastException/Overview/ToString2.cs" interactive="try-dotnet" id="Snippet5":::
+ :::code language="fsharp" source="~/snippets/fsharp/System/InvalidCastException/Overview/ToString2.fs" id="Snippet5":::
 
 <a name="Migration"></a>
 ## Visual Basic 6.0 migration